GB2227742A - Difluorinated terphenyls and their use in liquid crystal materials - Google Patents

Abstract

Difluorinated terphenyls of formula I are described, together with their use in nematic and ferroelectric smectic C liquid crystal materials. <IMAGE> wherein R1 and R2 are independently alkoxy, alkyl, perfluoroalkoxy or perfluoroalkyl; any one of the following pairs of lateral substituents both being fluorine: (A, B), (C, D), (D, E), (C, E), (B, G), (D, J), (D, K), (A, G), (C, J) all of the other lateral substitution positions being occupied by hydrogen, but excluding the terphenyl in which (C, D) are both fluorine, R1 is ethoxy and R2 is n-pentyl.

Description

DIFLUORINATED TERPHENYLS AND THEIR USE IN LIQUID CRYSTAL MATERIALS This invention relates to novel laterally difluorinated terphenyls and their use in liquid crystal materials.

Liquid crystal materials are well knonw, and generally exploit the electro-optical switching properties of the nematic (N) or smectic, especially chiral smectic C (sic) or smectic I (so), phases, the asterisk denoting a chiral phase. They are used widely in electrooptical display devices.

Such materials are generally mixtures of compounds selected so that the mixture shows desirable properties. In particular such properties include: (i) A broad temperature range over which a suitable liquid crystal phase, eg SA, Sc, Sc, SI, SI or N persists, this range preferably including room temperature (ca 200C).

(ii) Low viscosity.

(iii) Ease of manufacture.

(iv) Good electro-optical response.

(v) In the case of compounds or mixtures which shown Sc phase, miscibility with one or more optically active compounds, ie which contain an asymmetrically substituted carbon atom, to form a helical chiral phase having a long pitch and a high spontaneous polarisation coefficient Ps. It is also useful if the compound or mixture shows an SA phase at a higher temperature than its Sc phase to assist in aligning the Sc phase with the electrodes of a liquid crystal electrooptical device.

Fluorinated terphenyls are known for use in liquid crystal materials. For example: EP-A-8430494.3 describes the preparation and use of monofluorinated terphenyls of

general formula: Qx where R1 and R2 are independently alkyl or alkoxy, in nematic liquid crystal materials. GE-A-8725928 and wo/07890 disclose the use of these monofluorinated terphenyls in S* mixtures.

EP-A-0084194 contains a wholly speculative reference to laterally difluorinated terphenyls, including a theoretical reference to the compound:

for use in nematic mixture. PCT/EP87/00515, which at the date of this patent application was unpublished, contains a speculative general formula which would include difluoroterphenyls, and also refers specifically to the two compounds:

used exclusively in nematic liquid crystal mixtures.

This invention seeks to identify other useful di fluorinated terphenyls, and in particular to investigate their use in smectic liquid crystal materials.

According to the invention, a novel di fluorinated terphenyl is provided, of general formula I:

in which terminal substituentsR1 and R2 are independently alkoxy, alkyl perfluoroalkyl or perfluoroalkoxy; any one of the following pairs of lateral substituents may both be fluorine (A,B), (C,D), (D,E), (C,E), (B,G), (D,J), (D,K), (A,G), (C,J), all of the other lateral substitution positions being occupied by hydrogen, but excluding the terphenyl in which (C,D) are both fluorine, R1 is ethoxy and R2 is n-pentyl.

The structural preferences discussed below are inter alia on the basis of usefulness in liquid crystal mixtures, and/or ease of preparation.

Preferred overall structures for the terphenyl of formulas are listed below in table 1.

Table 1

In terphenyls of formula I, R1 and R2 preferably each independeftly contain up to 15 carbon atoms, most preferably 5 to 12 carbon atoms.

R1 and R2 may be straight chain, branched chain or may contain an asymmetrically substituted carbon atom (designated herein C*). R1 and R2 are preferably independently n-alkyl or n-alkoxy. Preferred alkyl or alkoxy groups containing an asymmetric carbon atom are (+) or (-) 2-methylbutyl, 2-methylbutyloxy, 3-methylpentyl , 3-methylpentyloxy, 4-methyLhexyl, h-methylhexy loxy, l-methyhlheptylor l-methylheptyloxy, and such groups may be present in an optically active or racemic form.

Terphenyls of formula I may for example be prepared using general routes to 9 shown schematically in Figs 1 to 7 of the accompanying drawings. Although illustrated therein for cases in which R1 and R2 are alkyl or alkoxy, it will be understood that perfluorolalkyl or perfluoroalkoxy analogues may be made by analogous routes. Other methods of making these compounds will be apparent to those skilled ir the art. Terphenyls of formula I in which one of the pairs (D,K) or (C,J) are both fluorine may for example be made using the starting difluorophenol of route 9, or the known l,3-difluoro-2-amino phenol, and adding appropriately 4-substituted phenyl rings to such precursors, using for example routes which couple these rings via known phenylboronic acids.

Terphenyls of formula I often show nematic or smectic C phases which persist over a broad temperature range and are useful constituents of liquid crystal mixtures.

Therefore according to a second aspect of the invention there is provided a liquid crystal material, being a mixture of compounds, at least one of which is a terphenyl of formula I, preferably one selected from table 1.

When the liquid crystal material is a nematic liquid crystal material, the other constituents of the material may be selected from a wide variety of compounds which are known to be useful constituents of nematic liquid crystal materials, for example those structural types listed in table 2, where RA and RB are independently alkyl or alkoxy containing 1 to 15 carbon atms: Table 2

Generally a nematic liquid crystal material of this aspect of the invention contains up to about 25% by weight of a terphenyl of formula I. For twisted nematic (TN), Freedericksz effect, cholesteric to nematic phase change effect devices, the bulk of the material may usefully comprise compounds selected from formulae 2.1 to 2.6. If a cholesteric phase is required, one or more of the alkyl groups R A or RB may contain an asymmetric carbon atom, eg in a 2-methylbutyl group.

Certain terphenyls of formula I have been found to be particularly useful in liquid crystal materials which employ the electrically controlled birefringence (ECB) effect (see for example M F Schieckel and K Fahrenschon "Deformation of nematic liquid crystals with vertical orientation in electrical fields" Appl Phys Lett. 19, (1971), 3912). In such materials one or more terphenyls of formula I may constitute up to about 20% by weight, typically up te about 10%. The bulk of such a mixture may usefully comprise compounds selected from table 3, in which RA and RB may be alkyl or alkoxy: Table 3

Certain terphenyls of formula I have been found to be useful components of liquid crystal materials which exploit the ferroelectric properties of the Sc phase. Certain terphenyls of formula I show smectic C phases which persist over a broad temperature range. Therefore this invention provides a liquid crystal material which shows an phase which is a mixture containing one or more terphenyls of formula I, and which may consist wholly of two or more terphenyls of formula I.

To provide an Sc phase, one of the constituents of this mixture must contain an asymmetric carbon atom, and this constituent may itself be a terphenyl of formula I, but is preferably a compound not of formula.

In Sc and Sc mixtures of this aspect of the invention, terphenyl of formulae 1.1, 1.2 and 1.4 are preferred.

When the Sc or Sc material of this aspect of the invention does not consist wholly of terphenyls of formula I, other constituents are compounds which are known to be useful constituents of Sc and/or Sc liquid crystal materials. A useful Sc liquid crystal material may comprise a mixture of one or more terphenyls of formula I, plus one or more other compounds which contain an asymmetrically substituted carbon atom.

In an Sc mixture of this aspect of the invention, R1 and R2 are preferably of a longer carbon chain length than would be used for nematic materials, for example each preferably contains 5 or more carbon atoms. R1 and R2 are preferably n-alkyl or n-alkoxy in such mixtures.

The discovery that SC mixtures may be prepared using terphenyls of formula I, and their advantages, ie good SC phases and fast switching speeds, are wholly unecpected over the prior art which refers exclusively to nematic or ECB mixtures. Indeed nematic or ECB mixtures are generally designed to exclude compounds which show smectic character.

Preferred compounds containing asymmetric carbon in an S material of this aspect of the invention include the l-methylheptyl esters disclosed in EP-A-0110299, or one or more of the compounds * containing a -COO.CH(CN) group disclosed in WO 87/07890 or in PCT Application PCT/GB 88/01111, for example compounds of formula:

where RA and R3 are as defined above, RB being preferably C1-C4 n-alkyl, cycloalkyl or branched alkyl. (F) indicates that the compound may carry one or more lateral fluoro-substituents.

RA in the last-above formula is preferably C5 - C12 n-alkyl or n-alkoxy, particlualy n-octlyoxy. RB is preferably methyl or a grout of general formula:

where a is O or an integer 1 - 6, and each of b and c are independently integers I - 6, preferably at least one of b or c being 1.

When the Sc mixture of this aspect of the invention contains two or more compounds which contain an asymmetric carbon aton, then two or more of these compounds may usefully be of opposite optical handedness, ie having (+) and (-) otical rotation Xr D and L stereoisomerism, In this way the length of the helical Sc pitch may be controlled, and/or a useful 5A phase may be induced, assisting alignment of the liquid crystal material with the electrodes of an electro-optic device.

The liquid crystal materials of this invention may be used in liquid crystal electro-optical display devices of known construction.

The invention will now be illustrated by way of example only with reference to accompanying figs 1-7 which show preparative routes 1-9 referred to above.

The following abbreviations are used: K = solid crystal N = nematic liquid crystal SA = smectic A liquid crystal SC = smectic C liquid crystal I = isotropic liquid Examples 1 - 10.

1. Preparation of:

A solution of l-bromohexane (60g) in acetone (150 ml) was added dropwise to a stirred mixture of 4-bromophenol (71g) and K2C03 (120g) in acetone (600 ml) at room temperature. The stirred mixture was heated under reflux for 43 hr (ie until glc revealed complete reaction).The product was extracted into ether twice, and the combined ethereal extracts were washed with water, 5% NaOH water and dried (Mg so4). The solvent was removed in vacuo and the residue was distilled (bp = 100-1100C at O.lmm Hg) to yield a colourless liquid (79.4g, 86)

A solution of the Grignard Reagent prepared frorr. IA (72g) and Mg (7.75g) In dry THF (250 ml) was added dropwise to a stirred, cooled (-780C) solution of tri-isopropyl borate (lO9.lg) in dry THG (40 ml) under dry N2.The stirred mixture was allowed to warm to room temperature overnight and stirred with 10% HCL (320 ml) at room temperature for 1 hr. The product was extracted into ether twice, and the combined etheral extracts were washed with water and dried (Mg SOb).

Solvent was removed in vacuo to yield a colourless solid (61.2g, 99%) mp = 80-85 C.

N- Bromosuccinimide (42g) was added in small amounts over 1 hr to a stirred, cooled (-100-00C) solution of 2-5-difluoroamiline (30-96g) in dry CH2 C12 (180 ml). The mixture was stirred at OOC for 2 hrs. The red solution was washed with a large amount of water twice, and dried (Mg S04). The solvent was removed in vacuo to yield a red solid (47.6keg) 95%, mp = 74-75 C.

A solution of 1C in dry benzene (200 ml) was added dropwise with stirring, over 1 hr to a stirred, cooled (ooh) solution of isopen tylnitrile (33.6g) in dry benzene. The mixture was heated under reflux for 1 hr and cooled. The product was extracted with ether twice and the combined organic layer was washed successively with water,aqueous sodium hydrogen carbonate, 2M hydrochloric acid, and water, and dried (Mg SO). The solvent was removed in vacuo and the crude product was steam distilled to give a brown-black solid. This was further purified by column chromatography (silica gel/ dichloromethane) to give a dark brown low melting solid (13.2g, 22%).

AlC13 (25.4g) was ground and added to a stirred, cooled (ooh) solution valeryl chloride (34.9g) in dry dichloromethane (120 ml). A solution of ]D (13.2g) in dry dichloromethane (120 ml) was added dropwise over 2 hr at 0 C. The mixture was stirred at room temperature for 48 hr and poured onto crushed ice/conc. HCL. The separated aqueous layer was washed with CH2C12 twice, the combined organic layers were washed with water, NaNC03, and water, and dried (MgS04).The solvent was removed in vacuo to yield a dark red oil which was distilled under reduced pressure (0.1 mm Hg, temperature not recorded) to give a low melting red-brown solid which was further purified by column chromatography (silica gel/CH2C12) to yield a low melting red-brown solid (8.0g, 46%)

Triethylsilane (7.0g) was added dropwise over 2 hr to a cooled, stirred (ooh) solution of 1E (8.0g) in trifluoroacetic acid (40 ml).

The reaction mixture was stirred at room temperature overnight and poured into Na HC03 solution. The product was extracted into ether twice and the combined ether layers were washed with water and dried (Mg S04). The solvent was removed in vacuo to yield an orange-brown oil. The crude product was distIlled under reduced pressure (short path, 110-1200C at 0.01 mm Hg) to give a red oil (5.50g, 70%).

A solution of 1B (0.9806g) in ethanol (15 ml) was added dropwise to a stirred mixture of 1F (1.25g) and tetrakis (triphenylphosphine) palladium (o) (0.1392g) in benzene (20 ml) and 2M-Na2C03 (20 mi) at room temperature under dry N2. The stirred mixture was heated under reflux (90-950C) for 23 hr (ie until glc analysis confirmed absence of starting materials). The mixture was colled, optionally stirred with 30,0 H202 (2 ml) for 1 hr at room temperature. The product was extracted with ether twice and the combined organic extracts were washed with brine and dried (Mg S04).The solvent was removed in vacuo and the residue was purified by column chromatography (silica gel/petroleum ether (bp 40-600C) - dichloromethane, 3-1) to give a colourless solid which was recrystallised from ethanol to give colourless plates. (0.72g, 45%).

2. Preparation c

Pentanol chloride (50g) was added dropwise to a stirred, cooled (ooh) mixture of bromobenzene (150 ml) and aluminium chloride (02g).

The mixture was stirred at OOC for 1 hr, heated at 800C for 2 hr, cooled and poured into 18% hydrochloric acid. The product was extracted into CHC13 twice, the combined organic extracts were washed with water and steam disilled to remove chloroform and the excess of bromobenzene. The product was extracted into chloroform twice, the combined organic phases were washed with water and dried (Mg S04).

The solvent was removed in vacuo and the residue was distilled (bp 180-1840C at 20 mm Hg) to yield a colourless solid (78.lg, 78%).

A mixture of 2A (77.lg), hydrazine hydrate (46.4g) and KOH (590g) in diethylene glycol (250 ml) was heated at 1300C for 2 hr, the excess of hydrazine hydrate was distilled off and the temperature was raised to 2000C for 2 hr. The cooled mixture was poured into 18% HCL, the product was extracted into ehter twice and the combined ethereal extracts were washed with water and dried (Mg S04). The solvent was removed in vacuo and the residue was distilled (bp 1451480C at 20 mm Hg) to yield a colourless liquid (58.1g, 80%).

The same method as for 1B was used.

Quantities: 2B 24.0g Magnesium 2.95g Tri-isopropylborate 39.8g yield: 19.3g, 95%

The same method as for 1G was used.

Quantities: 1F 1.25g 2C 0.8604g Tetrakis (triphenylphosphine) palladium (0) 0.14g.

The cruide product was purified by column chromatography (silica gel/petroleum fraction (bp 40-60 C) - dichloromethane, 1:1) to yield a colourless solid which was recrystallised from ethanol to yield colourless plates. (0.56g, 37%).

3. PreParation of:

A solution of l-bromohexane (9.33g) in acetone (20 ml) was added dropwise to a stirred mixture of 4-bromo-3-fluorophenol (9.OOg) and potassium carbonate (13.5g) in acetone (75 ml) at room temperature.

The stirred mixture was heated under reflux for 21 hr (ie until glc analysis revealed a complete reaction). The product was extracted into ether twice, and the combined ether extracts were washed with water, 10% sodium hydroxide, water and dried (Mg S04). The solvent was removed under vacuo and the residue was distilled (bp 100-1050C at 0.1 mm Hg) to yield a colourless liquid (12.7g, 98%)

A solution of n-butyllithium (10.OM in hexane, 3.30 ml) was added dropwise to a stirred colled (-780C) solution of 3A (9.or) in dry THF (70 ml) under dry N2 .The stirred mixture was maintained under these conditions for 2.5 hr and then a colled solution of tri-isopropyl borate (11.28g) in dry THF (50 ml) was added dropwise at -780C. The stirred mixture was allowed to warm to room temperature overnight and then stirred for 1 hr at room temperature with 10% HCL (50 ml). The product was extracted into ether twice and the combined ethereal extracts were washed with water and dried (Mg S04). The solvent was removed in vacuo to afford an off-white solid (7.3g, 99%).

The method used was as for 1G.

Quantities: 4' -bromo-2-fluoro-4-pentylbiphenyl 1.45g 3B 1.30g Tetrakis (triphenylphosphinez palladium 0.169g The cruide product was purified by column chromatogrph (silica gel/petroleum fraction (bp 40-600C)-dichloromethane 3:1) to give a colourless solid which was recrystallised from ethanol to give colourless waxy plates.

(4')-bromo-2-fluoro-4-pentylbiphenyl is commercially available (BDHAtd).

4. Preparation of t- (s H s) o XrXW cS H 4A n - i ttnC) The method used was as for 3A Quantities: 4-bromo-3-fluorophenol 6.00g l-bromooctane 7.30g K2 CO3 l0.00g Product was distilled under reduced pressure (bp =-140-142 C at 0.5 mm Hg) to yield a colourless liquid (9.0lg, 96%).

The method used was as for 3B Quantities: 4' -bromo-2-fluoro-4-pentylbiphenyl 9. 90g Magnesium 0.871g Tri-isopropylborate 11.66g (crude yield 8.85g, 100%)

The method used was as for 1G Quantities: 4A 6. wog 4B 1.75g Tetrakis (triphenylphosphine) palladium (0) 0.2979g The crude product was purified by column chromatugraphy (silica gel/ petroleum fraction (bp 40-60 C) - CH2 C12 6:1) to give a colourless solid which was recrystallised from ethanol to yield colourless Dlates (1.57R 55%).

5. Preparation of ,Hvso < Cs n t 5A Cg C) The method was as for 4A Quantities: 4-bromo-2-fluorophenol 10 . Og l-bromohexane 10.37g K2 C03 14.5g Yield 13.71g 96%

The method was as for 1G Quantities: SA 1.35g 4B 1.77g Tetrakis (triphenylphosphine) palladium (0) 0.2991g The cruide product was purified by column chromatography (silica gel/ petroleum fraction (bp 40-600C) - CH2 C12 6:1) to give a colourless solid which was recrystallised from ethanol-ethyl acetate (10:1) to yield colourless plates (l.lOg, 51%).

F 1 6. Preparation of n- C O H\D Cs H FF 6A The method used as for 3B Quantities: 1,2-difluorobenzene 7.50g (from Fluorochem) n-butyllithium 6.60 ml, lO.OM in hexane triisopropylborate 24. 82g

The method used was as for 1G Quantities: l-bromo-4-pentylbenzene 3. 80g 6A 3.50g Tetrakis (triphenylphosphine) palladium (0) 0.651g Coupling to give biphenyls was found to be faster than for terphenyls so this reaction was complete within 5 hr.

The cruide product was purified by column chromatography (silica gel/petroleum fraction (bp 40-600C): CH2 C12 3:1) to yield a colourless liquid (4.3g, 99%).

The method used was as for 3B Quantities: 6B It. OOg n-butyllithium 1.50 ml, 10.OM in hexane tri-lsopopylborate 5.70g Yield = h.50g, 99 as colourless solid.

The method used was as for 1G Quantities: 1B 1.30g 2.0g Tetrakis (triphenylphosphine) palladium (o) 0.312G The cruide product was purified by column chromatography (silica gel/ petroleum Pro-ition (bp 40600C): dichloromethane 6:1) to yield a colourless solid which was recrystallised from ethanol to give colourless plates (l.lOg, 50%).

The analogous compound 6E:

was prepared using an analogous route in which l-bromo-4-octyloxybenzene was used instead of 13. This compound was prepared by the same method as for 1B: Quantities: 4-bromophenol 64.54g l-bromooctane 60.00g K2C03 103.5g Yield = 86.5g, 98% as a colourless liquid bp = 1450C at 0.1 mm Hg.

In the preparation of 6E the method used was as for 6D.

Quantities: l-bromo-4-octoxybenzene 1. 40g 6e l.90g Tetrakis (triphenylphosphine) palladium (0) 0.3102g The cruide product was purified by column chromatography (silica gel/ petroleum fraction (bp 40-60 C)- CH2 C12, 5:1) to give a colourless solid which was recrystallised from ethanol-ethyl acetate (4:1) to yield colourless plates (1.75g, 77%).

7. Preparation of I -1 I -c 4Q t't The method used was as for 1G.

Quantities: 23 1.30g 6e 2.10g Tetrakis (triphenylphosphine) palladium (0) 0.2 & The cruide product was purified by column chromatography (silica gel/ petroleum fraction (bp 40-60 C)- CH2 C12, 5:1) to yield a colourless solid which was recrystallised from ethanol to give colourless plates (1.27g, 55).

8. Preparation of h cc S-CE,n. ^ FF 8A The method used was a modification of MF Hawthorne J Org Chem (1957), 22, 1001.

Quantities: 6A 4.40g 10% hydrogen peroxide 30 ml Yield: 2.01g, 80% off-white solid, mp 34-36 C.

(Compound 8A is also supplied by Fluorochem Ltd)

The method used was the same as for 3A.

Quantities: 8A 7.OOg l-bromohexane 10.72g K2 C03 17.40g The crude product was distilled (bp 12200 at 15mm Hg) to give a colourless liquid (ll.lOg, 96%).

The method was as for 3B.

Quantities: 8B 10. Og n-butyllithium 4.70ml, 10.OM in hexane Tri-isopropylborate 17. 70g Yield 12.10g, 100% colourless solid.

The method was as for 1G Quantities: 4-bromo-41-pentylbiphenyl 1. 40g 8e 1.50g Tetrakis (triphenylphosphine) palladium (0) 0.2868g The crude product was purified by column chromatography (silica gel/ petroleum fraction (bp 40-60 C): CH2 C12, 3:1) to give a colourless solid which was recrystallised from ethanol -ethyl acetate (10:1) as colourless crystals. (1.65g, 82).

was prepared by an analogous route using 1,2-difluoro-3-octoxybenzene instead cf 8B. This was prepared using the method as for 3A.

Quantities: 8A 7.OOg l-bromooctane 12. 55g K2 C03 17.40g The cruide product was distilled (bp 1500C at 15mm Hg) to give a colourless liquid (8.90g, 68%).

To prepare 8E using this:

method as for 8C.

Quantities: l,2-difluoro-3-octoxybenzene 7. 50g n-butyllithium 3.10ml lO.OM in hexane triisopropylborate 11.66g Yield = 9.00g, 100% colourless solid

method as for 8D Quantities: 4-bromo-41-pentylbiphenyl 1. 54g 2, 3-difluoro-4-octoxyphenylboronic acid 1. 75g Tetrakis (triphenylphospine) paladium (0) 0.309g The crude product was purified by column chromatography (silica gel/ petroleum fraction (bp 40-600C) dichloromethane, 3:1) to give a colourless solid which was recrystallised from ethanol-ethyl acetate 4:1 to give colourless crystals C1-97g 84%).

9. Preparation of

A solution of pentanal (l9.Og, 0.22 mol) in dry ether (75 ml) was added dropwise to a stirred solution of the Grignard reagent at room temperature, under dry nitrogen, prepared from l-bromo-3,3-difluoro benzene (50.2g, 0.26 mol) and magnesium (7.25g, 0.30 mol) in dry THF (100 ml). The stirred mixture was heated under reflux for 2 h, cooled and a saturated solution of ammonium chloride (300 ml) was added. The product was extracted into ether (twice), and the combined ethereal extracts were washed with water and dried (MgS04). The solvent was removed in vacuo to give a pale-orange liquid (51.lg) which was distilled to yield a colourless liquid.Smaller quantities of crude product were purified by column chramatography (silica gel/ dichloromethane) to yield a colourless liquid (92).

Yield 35.8g, 69% bp 900C at 0.5 mm Hg

Phosphorus(V) oxide (64.5g, 0.45 mol) was added in portions to a stirred solution of compound 9A (35.0g, 0.175 mol) in dry pentane (150 n2) at room temperature. The mixture was stirred at room temperature overnight (glc analysis revealed absence of starting material) and filtered.

5% Palladium-on-charcoal (4.0g) was added to the above filtrate [ie compound 9B in pentane (150 ml)j at room temperature. The stirred mixture was hydrogenated at atmospheric pressure for 4 h (ie, until glc analysis revealed absence of starting material) and the mixture was filtered. The majority of the pentane was removed in vacuo, and the final amount of pentane was distilled off (760 mm Hg) at 380C and the residue was then distilled to yield a colourless liquid.

Yield 23.4g, 73% bp 2000C at 760 mm Hg

A solution of n-butyllithium (10.4 M in haxane; 2.70 ml, 0.028 mo.) was added dropwise to a stirred, cooled (-780C) under dry nitrogen.

The stirred mixture was maintained under these conditions for 2.5 h and a previously cooled solution of tri-isopropyl borate (10.22g, 0.054 mol) in dry THF (50 ml) was added dropwise at -780C. The stirred mixture was allowed to warm to room temperature overnight and stirred for 1 hr with 10% hydrochloric acid (30 ml). The product was extracted into ether (twice), and the combined ethereal extracts were washed with water and dried (MgS04). The solvent was removed in vacuo to give a colourless solid.

Yield 6.7g, 100/o mp 95-1000C

The method used was as for 1G.

Quantities: 4-bromohexoxybiphenyl 1. 30g 9D l.l0g Tetrakis (triphenylphosphine) palladium (0) 0.157g The crude product was purified by column chromatography (basic aluminia/ petroleum fraction (bp 40-60 C) with the gradual introduction of dichloromethane) to give a colourless solid which was recrystallised from ethanol to give colourless plates (0.20g 12%).

The method used was as for 1G Quantities; 4-bromo-41-pentylbhenyl 1. 40g 9D 1.37g Tetrakis (triphenylphosphine) palladium (0) 0.157g The crude product was purified by column chromatography (silica gel/ petroleum fraction (bp 40-600C) - CH2 C12, 1:1) to give a colourless liquid which contained a solid. The solid was filtered off and washed with petroleum fraction (bp 40-60 C). The solvent was removed in vacuo to give a colourless liquid, two impurities were removed by using a Hugelrohr distillation apparatus to give a colourless solid which was recrystallised from ethanol to yield colourless crystals (O.l9g, 10%).

The following table lists difluoroterphenyls prepared using routes 1 to 10.- In each case the compounds are shown to have potentially useful liquid crystal phases, eg N or Sc, which in some cases persist over a broad temperature range.

Difluoroterphenyls Prepared using routes 1 - @.

Formula Liquid crystal transitions Route r - CS H > C5d(~~ K 60 N 120 I 7 F F Cs4 0 X&commat; cos HXl- K 53 SC 65.5 N 149 1 6 F K w CsH N K 48.5 SC 95.1 N 141.5 I 6 1= 1 C'- > &commat; CS~6 K 97.5 so 145.5 N 1661 B 144 148 8 A- cos cos H1^N K 93.5 SC 144 5A 148 N 1591 F n-coXyo-csti - K 45 N 131 1 3 K 42.5 N 121.5 I 4 P F:: K 96 SC 1055 N 139 I 5 A C c\t,3C) < E K 96 S0 105.5 N 139 1 5 r'- - CS l > Cs H n- K 63 N 85 I 2 ss O C6 C5d ' K 51 N 117 I 1 F f'- CH, 4 < CS H K 50 N 32 I 9 "- - K 62 N 123 1 9 Example 10 Ferroelectric smectic C liquid crystal mixtures containing 1ifluoroterphenyls.

Mixture lOA (D-C F 1-" F n- CeH170 XX C5 1 n 95 wt % I / CH3 (+)- n- Cw-.170- O4 -COOCHCH 5 wt % OH3 The optically active compound in this mixture is of L configuration.

The mixture showed the liquid crystal transitions ( C) K 85.9 SC 125.4 SA 143.2 N 150.6 I The SC phase supercooled to 76 C.

Temp ( C) Ps(nCcm-2) SC tilt( ) 125 4.0 16.0 122 6.6 120 7.8 18.0 115 113 10.6 110 11.4 22.5 105 13.1 100 14.6 25 95 16.0 27 90 16.9 28 87 17.6 85 18.1 82 18.8 19.0 130 1.0 Mixture 10B

Mixture 1CB (contd.) CN CH n-C,H1 I I (+)-n-CRH170 ee -COOCHCH 6.25 wt % OH CN CH3 (-)-n-C8H170 e 3 &commat; -COOCHCH 3.75 wt % CH3 The mixture showed the following liquid crystal transitions (00): # 20 SC 84.7 SA 98.6 N 128 I ie the mixture showed a room temperature SC phase.

Temp.(0O) Ps(nCcm 2) SC tilt (0) 84 0.12 82 1.12 9.0 80 2.0 10.0 75 2.93 14.0 70 3.75 15.0 65 4.32 60 4.87 18.0 55 5.4 50 5.83 20.0 45 6.4 40 6.9 22.5 35 7.28 22.5 30 7.74 23.5 25 8.08 Using a liquid crystal electro-optic cell of well known cons truction, mixture lOB showed a swtching time of about 100 psec with a 20 V applied voltage, and a 2 jim spaced cell with polyimide ali gnment films.

Example 11 A 1:1 by weight mixture of:

shoed an SC phase which supercooled to 28 C, SC 79.1 N 142.4 I. The birefringence of the mixture was 0.19.

Claims (17)

1. A difluorinated terohenyl of formula:

wherein R1 and R2 are independently alkoxy, alkyl, perfluoroalkoxy or perfluoroalkyl; any one of the following pairs of lateral substituents being both fluorine: (A, B), (C, D), (D, E), (C, E), (B, G), (D, J), (D, K), (A, G), (C, J) all of the other lateral substitution positions being occupied by hydrogen, but excluding the terphenyl in which (C, D) are both fluorine, R1 is ethoxy and R2 is n-pentyl.

2. A terphenyl according to claim 1 having a formula:

3. A terphenyl according to claim 1 having a formula:

4. A terphenyl according to claim 1 having a formula:

5. A terphenyl according to claim 1 having a formula:

6. A terphenyl according to claim 1 having a formula:

7. A terphenyl according to claim 1 having a formula:

8. A terphenyl according to any one of claims 1 to 7 wherein F and R2 each independently contain 1 - 15 carbon atoms.

9. A terphenyl according to claim 8 wherein each of R1 and R2 independently contain 5 - 12 carbon atoms.

10. A terphenyl according to any one of claims 1 to 9 wherein R1 and R2 are each independently n-alkyl or n-alkoxy.

11. A liquid crystal material, being a mixture of compounds, at least one of which is a terphenyl as claimed in claim 1.

12. A liquid crystal material, being a mixture of compounds, at least one of which is a terphenyl as claimed in any one of claims 2 to 10.

13. A liquid crystal material according to claim 11 or 12, being a nematic liquid crystal material.

14. A liquid crystal material according to claim 11 or 12, being a liquid crystal material.

15. A liquid crystal material according to claim 14 which additionally also contains a compound of formula:

where RA is alkyl or alkoxy and RB is alkyl, and (F) indicates that the ring may carry one or more lateral fluorosubstituents.

16. A liquid crystal device which uses a liquid crystal material according to any one of claims 11 to 15.

17. A difluorinated terphenyl according to any one of claims 1 to 10 as described in any one of examples 1 - 9 herein.